package common;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.math.BigInteger;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;

/**
 * 实现MD5计算
 * @author maojj
 *
 */
public class MD5
{
	/**
	 * 实现MD5计算
	 * @param file - 需要计算MD5的文件
	 * @return 文件MD5值
	 * @throws FileNotFoundException
	 */
	public static String getMD5(File file) throws FileNotFoundException
	{
		String value = null;
		FileInputStream in = new FileInputStream(file);
		try
		{
			MappedByteBuffer byteBuffer = in.getChannel().map(FileChannel.MapMode.READ_ONLY, 0, file.length());
			MessageDigest md5 = MessageDigest.getInstance("MD5");
			md5.update(byteBuffer);
			BigInteger bi = new BigInteger(1, md5.digest());
			value = bi.toString(16);
		}
		catch (Exception e)
		{
			e.printStackTrace();
		}
		finally
		{
			if (null != in)
			{
				try
				{
					in.close();
				}
				catch (IOException e)
				{
					e.printStackTrace();
				}
			}
		}
		return value;
	}
}
